1. Field of the Invention
The present invention pertains to the field of focused ion beam systems. More particularly, the present invention pertains to the design of optical columns used to produce a focused beam of ions on the surface of a target, blank the beam on/off, and deflect the beam in a controlled manner across a target surface.
2. The Prior Art
There are numerous processes which can be performed using focused ion beams including: ion implantation, resist exposure, repair of x-ray and photo masks, micromachining, and scanning ion microscopy and microanalysis.
A typical example of the prior art is given in U.S. Pat. No. 4,563,587 "Focused Ion Beam Microfabrication Column". One key element of this reference is the requirement that the beam energy is not increased substantially by the low aberration focusing means. In fact, this reference states that the aberrations due to the mass filter are reduced by using lower beam voltages through the mass filter, when, in fact, the opposite is the case. Another feature of this reference is the positioning of an energy control means at the beam crossover. A pair of spaced electrodes functions as the final electrostatic focus/accelerating means, in which the beam must be accelerated substantially in order to achieve the required focusing action.
A second example of the prior art is U.S. Pat. No. 4,556,798 "Focused Ion Beam Column". A key element of this reference is the use of a second lens which is always accelerating. In addition, the deflection angle of the beam is specified not to exceed 10 mrad and the beam energy is required to increase through the first and second lenses at substantially operating equal ratios.
U.S. Pat. No. 4,479,060 "Apparatus for Irradiation with Charged Particle Beams" describes an ion column which includes at least one magnetic lens. U.S. Pat. No. 4,457,803 "Processing Method Using a Focused Ion Beam" describes a system in which the etching depth is preset in control device.